8 September 2016 under-frequency event

The Authority received a report from the system operator that recommended that the causer of the 8 September 2016 under-frequency event was Transpower New Zealand Limited.

No submissions on the draft determination were received. Accordingly, the Authority’s final determination under clause 8.61(9) of the Code is that Transpower, as grid owner, is the causer of the under-frequency event on 8 September 2016.

The Authority’s reasons for this final determination are:

• the interruption/reduction of energy on 8 September 2016 occurred at the Maraetai bus, which is a set of assets belonging to Transpower as the grid owner
• no other asset was identified as having caused or potentially caused this under frequency event
• in the system operator’s view, Transpower, as grid owner, is the causer of this under-frequency event
• the system operator wrote to Transpower (on 15 September 2016) setting out its view that the event was initiated at the Maraetai bus resulting in a loss of injection from Maraetai and Waipapa power stations, and seeking any information Transpower could provide
• in a reply to the system operator (dated 22 September 2016), Transpower has accepted that, as grid owner, it is the causer of this event.
• having considered the system operator’s report and the relevant elements of the Code, the Authority (based on the information available to it at this time) concurs with the system operator’s findings.

In accordance with clause 8.65 of the Code, the clearing manager will rebate the $238,375 event charge to relevant generators and the HVDC owner.